This invention relates to a laser drive apparatus for controlling the emission intensity of a laser output.
In a print apparatus such as the laser-beam printer which forms a toner image on a recording paper by the electrophoto-graphic copying method, the concentration of the image formed on the recording paper is expressed by the assignment of intensity levels and the assignment of intensity levels is effected, for example, by varying the size (area) of each dot of the image. Since the size of each dot can be varied by varying the emission intensity of a laser beam, the practice of modulating the laser output itself in accordance with intensity levels has been in vogue in the reproduction of an image.
The method heretofore adopted for controlling the emission intensity of a laser output by intensity levels as described above has comprised preparing a .gamma. compensation ROM in which intensity levels to be controlled has been written as data, retrieving pertinent data stored in the ROM to ensure generation of such laser outputs as permit reproduction of linear gradation, and controlling the laser outputs on the basis of the retrieved data.
Since the conventional modulation of the intensity of a laser output relies on the control of the laser output according to the data stored in the ROM as mentioned above, the laser using an input current of a fixed magnitude emits a varied emission when the output intensity of the laser is varied as when the laser output is varied by a change in temperature, for example. When ROM data so stored as to permit linear assignment of intensity levels are used, therefore, the problem is posed that the laser will fail to effect linear assignment of intensity levels as an output because the ROM data do not incorporate variations due to changes in temperature.